Do not include XHR in ajax messaging

Headers from response included as parsed object, XHR not directly
included
Remove debugger statements
Add 'read' event to observables

To enable the ability to know when an observable is read a new event
is published (hack using dependency detection). This will be used to
implement 'async' or 'deferred' reading without having to wrap an
observable in a computed
Add jasmine.slow for detecting slow tests
Stop using jasmine-dom-fixture

By using a custom implementation of fixtures which is *much*
simplified have been able to shave about 2s off of total test run time
in Chrome.
Remove $ajax HEAD support + tests

HEAD requests are inherently very different to the other verbs, so
remove until decisions on what should be supported here are made
Update jQuery to v1.10.0